1. Field of the Invention
The present invention relates to an image-forming apparatus, such as a mono-chrome/full-color copying machine, a printer, a facsimile and a composite machine thereof.
2. Description of the Related Art
In an image-forming apparatus of an intermediate transfer system in which toner images of respective colors, formed on latent-image supporting members, are respectively primary-transferred, and superposed on an intermediate transfer member, and then secondary-transferred onto a image receiving medium at one time, such an image-forming apparatus which uses an intermediate transfer member having a hard releasing layer formed on the surface thereof so as to improve the releasing property to the toner, in order to improve the secondary transferring rate, has been proposed. With this arrangement, it becomes possible not only to improve the image quality, but also to reduce residual toner after the secondary-transferring process (waste toner) remaining on the intermediate transfer member after the secondary-transferring process; thus, it becomes possible to reduce the amount of waste toner to be discharged, and consequently to reduce the environmental load as well as loads imposed on the user, such as exchanging operations of waste-toner recovery containers.
In the above-mentioned image-forming apparatus, however, upon primary-transferring a toner image, formed on the latent-image supporting member, onto the intermediate transfer member, the toner image is sandwiched between the latent-image supporting member and the intermediate transfer member to be aggregated under a pressing force to cause a problem of occurrence of a void image. More specifically, as shown in FIG. 9, one portion 101 of the aggregated toner comes to have an increased adhesion strength to the latent-image supporting member 103 rather than to the intermediate transfer member having a higher releasing property, and is not primary-transferred to remain on the latent-image supporting member 103. In particular, in the center portion of a character image and a fine line image where a pressing force becomes higher to increase the toner aggregating force, the occurrence of a void image becomes conspicuous.
In the case when there is a temperature rise in the machine due to continuous printing operations or the like, components contained in the developer tend to easily adhere to the intermediate transfer member. Even in such a state, the adhered matter can be scraped together with toner by a cleaning blade or the like in the case of a small number of printing operations; however, when printing operations are continuously carried out, the components of the developer are kept adhering to the intermediate transfer member, with the result that the adhered matter is no longer scraped by the cleaning blade or the like to cause filming on the surface of the intermediate transfer member. The filming causes reduction in image quality and damage in the cleaning blade edge portion, resulting in insufficient cleaning.
In order to prevent occurrences of a void image and filming, it has been proposed that a speed difference is prepared between peripheral speeds of the intermediate transfer member and the latent-image supporting member (Patent Documents 1 and 2). However, this method tends to cause scratches on the intermediate transfer member and the latent-image supporting member, resulting in a new problem of degradation in image quality. This method fails to prevent filming sufficiently.    [Patent Document 1] Japanese Patent Application Laid-Open No. 6-317992    [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-113284